Giant photo-effect in proton transport through graphene

Graphene has recently been shown to be permeable to thermal protons, nuclei of hydrogen atoms, which sparked interest in its use as a proton-conducting membrane in relevant technologies. Here we report that proton transport through graphene can be enhanced strongly by iluminating it with visible light. Using electrical measurements and mass spectrometry, we find a photoresponsivity of ∼104 A W-1, which translates into a gain of ∼104 protons per photon, with response times in a microsecond range. These characteristics are competitive with thos of state-of-the-art photodetectors based on electron transport using silicon and novel two-dimensional materials. The photo-proton effect can be important for graphene's envisaged use in fuel cells and hydrogen isotope separation. Our observations can also be of interest for other applications such as light-iduced water splitting, photo-catalysis and novel photodetectors.